The present invention relates to a method for measuring the nip force and/or the nip pressure in a nip formed, e.g., by a revolving roll or a corresponding band employed in the manufacture of paper by utilizing a series of measurement detectors. The detectors are placed over a certain width in the transverse direction of the revolving roll or the band, preferably over the entire width of the paper web. The measurement signals obtained from the detectors are passed to a measurement amplifier unit having connectors coupled to the detectors. The connectors are controlled through the measurement amplifier unit so that the signal of each measurement detector is passed to a telemeter transmitter placed in connection with the revolving roll or equivalent. The telemetric messages is transmitted by the telemeter transmitter wirelessly and is received by a telemeter receiver placed outside the revolving roll or equivalent.
The present invention also relates to a device for measuring the nip force and/or the nip pressure and the distribution of the same in a nip formed by a revolving roll or by a corresponding band employed in the manufacture of paper. The device comprises a series of detectors placed in connection with the revolving roll or the band, preferably uniformly spaced in the transverse direction of the roll or the band. The device also includes a telemeter transmitter arranged in connection with the revolving roll or the band and to receive the signals obtained from the different measurement detectors. The device also comprises a telemeter receiver arranged in proximity to the telemeter transmitter outside the roll or equivalent for receiving the measurement signals transmitted by the telemeter transmitter without the use of wires, i.e., a wireless connection.
In a number of different stages in the manufacture of paper, various press nips are used through which the paper web is passed. Examples of such nips are roll nips and so-called extended nips in the dewatering press of a paper machine, calendaring nips, and nips in paper winders. The distribution of the pressure in a nip in a dewatering press in the transverse direction, i.e., the direction of the axes of the nip rolls, affects the transverse moisture profile of the web that is being pressed.
It is known in the prior art to use adjustable-crown rolls or so-called Kusters rolls as press rolls because in these rolls, the transverse distribution of the linear load in the press nip can be controlled by means of hydraulic loading members. These members are generally regulated on the basis of regulation signals given by moisture and/or grammage detectors. However, in view of overall control and regulation of the process, it would be extremely important to know the factual values and distributions of the nip pressure both in the transverse direction and in the machine direction. A further piece of information that is important for the control of the nip process is the width of the nip in the direction of running of the web, i.e., in the machine direction, because this information would permit an optimization of the pressing process. This information is also significant for the regulation of the nips in calenders and winders.
As an example of a prior art system for regulating press nips, reference is made to Finnish Patent No. 76,872 (corresponding to U.S. Pat. No. 4,791,863, the specification of which is incorporated by reference herein). The system of measurement in accordance with the present invention is usable, for example, in an environment similar to that described in patent FI 76,872.
In recent years, various so-called extended-nip presses have been introduced and used which are based on press shoes and/or on press belts. In these presses, the width of the press zone in the machine direction is substantially larger than in the roll nips proper. Also, in the case of extended-nip presses, the distribution of the nip pressure in the shoe and/or band nips both in the machine direction and in the transverse direction is an important parameter in view of the control of the pressing process. As one example of an extended-nip presses, reference is made to Finnish Patent No. 82,092 corresponding to U.S. Pat. No. 5,043,046, the specification of which is incorporated by reference herein.
In the prior art, various drum reel-ups are known in which belt support units have been employed in addition to carrier drums. In the reeling of the paper web, it is also important to know the values and distributions of the nip pressure both in the machine direction and in the transverse direction. As examples of drum reel-ups developed by the assignee, and in which the method and the device of the present invention can be used, reference is made to the assignee's Finnish Patent Nos. 81,768 and 81,770, corresponding to U.S. Pat. Nos. 4,921,183 and 4,883,233, respectively, the specifications of which are incorporated by reference herein.
The distribution of the nip force in the machine direction and in the transverse direction is important in the regulation and control of the paper manufacture process. However, it has been practically almost impossible to measure the nip force distribution by means of the prior art methods and devices during paper production operations. Measurement of nip forces from a revolving roll has been carried out under laboratory conditions, in which respect reference is made to an article in the journal Paperi ja Puu - Paper and Timber 73 (1991):5, J. Koriseva, T. Kiema, and M. Tervonen: "Soft Calender Nip: An Interesting Subject for Research and Measurement". In the method described in this paper, a number of detectors were installed on a roll, each of which requires a telemetric equipment of its own and amplifiers of its own. Since the weight of the measurement system consists primarily of the weight of the telemetric equipment (about 1 kilogram per channel), this, together with the high costs of such equipment, imposes a limitation on the number of the measurement channels and detectors in a factual roll in a paper machine or paper finishing machine. As a result of the limited space, it is, in practice, very difficult to fit a number of telemetric devices on a revolving roll in a paper machine or paper finishing machine without alterations in the construction.
Moreover, with respect to the prior art related to the present invention, reference is made to published International Patent Application WO 91/13337 (assigned to Beloit Corp.).
In the prior art methods and devices for measuring nip forces, further problems have developed in the calibration of the detectors as well as in the transfer of the signal from the revolving roll. In a manner known in the prior art, glide rings and equivalent arrangements in addition to telemetric equipment have been used to transfer the signal. However, this structure is complicated and susceptible to disturbances.
In view of eliminating the drawbacks stated above, in the assignee's Finnish Patent Application No. 914829 (Published Pat. Appl. No. 86,771), a method and a device closely related to the present invention are described in which the measurement signals received from the different detectors are passed to a switching unit. The connectors of the switching unit are controlled based on the rotation of the roll or equivalent by means of a pulse generator or equivalent so that, through the switching unit, the signal of each measurement detector is alternatingly connected to a telemeter transmitter placed in connection with the revolving roll or equivalent. By means of the telemeter transmitter, the series of measurement signals are transmitted wirelessly to a stationary telemeter receiver placed outside the revolving roll or equivalent.
FI 914829 describes a method and device for measuring the nip forces and/or the nip pressures and distributions of same in roll and/or band nips employed in the manufacture of paper so that the drawbacks discussed above can be substantially avoided. The measurement method and device of this reference is suitable for on-line measurement of nip forces and/or pressures during production operation. The transfer of the signals from the revolving roll is accomplished in this reference more simply and economically so that the method is suitable for a papermaking environment, which is quite demanding in this respect. The problems related to the location of the detectors on the nip roll or nip band are also substantially eliminated by the device of this reference.